The present invention relates to a self drilling blind rivet and a method for making same. More particularly, the present invention relates to a self drilling blind rivet including a mandrel adapted for carrying a short drill bit cold forged on a mass-production basis, and a method for making such drill bits on a mass-production basis.
The known self drilling blind rivet has a drill bit at the top end of a mandrel trapped inside of a hollow body. For example, Japanese Patent Publication No. 41--16724, No. 49--22967 and U.S. Pat. No. 4,293,258 disclose typical self drilling blind rivets of this type.
A disadvantage of these known rivets is the difficulty of mass-production and the increased production cost. More specifically, it is costly to make a one piece rivet in which a mandrel is trapped inside of the hollow body and provided with a drill having a larger diameter than that of the body. There is another method which makes short drill bits separately from the bodies and join them. However it is difficult to make short drill bits to exact dimensions. Although there is a large demand for blind rivets in the industry, the difficulty of mass production is a bottleneck in the supply.